Process for the separation of solids of different specific gravity and grain size



Feb. 27, 1951 M. cs. DRIESSEN ETAL 2,543,689

PROCESS FOR THE SEPARATION OF souns or DIFFERENT SPECIFIC GRAVITY AND GRAIN SIZE Filed April 23, 1946 l3 Q14 11 15 I l 7 Fig.2

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Patented Feb. 27, 1951 2.543389 PROCESS FOR THE SEPARATION OF SOLIDS OF DIFFERENT GRAIN SIZE SPECIFIC GRAVITY AND Driessen, Brunssum, and Centinus Krijgsman and Jan N. J. Leeman, Hoensbroek, Netherlands;

Antje G. Driessen, administrator of said Maximiliaan G.

Driessen, de-

ceased, assignors to De Direetie van de Staatsmijnen in Limburg,

Heerlen, Netherlands. Application April 23, 1946, Serial No.

In the Netherlands July 21, 1942 Section 1, Public Law Patent expire 9 Claims.

The present invention relates to a new and improved process for separating solid materials of diflerent specific gravity and diilerent grain size into fractions.

In practice it is often necessary to separate mixtures 01 solid materials of difierent character. In the mining industry, for example, the useful parts of the hauled or hoisted product must generally be separated. For this purpose advantage is taken of the different specific gravity oi the parts. For this separation according to specific gravity various processes are known. Coal and ore washeries, using the so-called floatand-sink process, are widely employed. In these washeries fluids having a true or apparent specific gravity intermediate the specific gravities of the parts which are to be separated are employed so that the parts of a lower specific gravity than that of the fluid float, while those of a higher specific gravity sink in the fluid.

The dimcuity of this process is that the resultant force which acts on the particles and which in the separating vessel determines the path of a particle having a specific gravity differing only little from the specific gravity of the separating fluid, is very small. This force is also very small for very small particles of higher specific gravity (which must sink), because the resistance against motion increases as the ratio 01' area to volume.

Attempts have been made to remove the difficulties of a static separation by introducing currents, but this in turn introduces the difflculty that a pure separation according to specific gravity is no longer obtained, since the separation is also influenced by the dimensions of the particles. These processes call for a preclassiflcation in grain sizes, which is the more diiilcult and complicated the smaller the dimensions of the material to be separated.

It is known that a so-calied cyclone or the type discussed in the article of Maximiliaan G. Driessen entitled "Cleaning of Coal by Heavy Liquids, with Special Reference to the Staatsmijnen- Loess Process" published August 1939, in the Journal of The Institute of Fuel, London, England, has a separating effect on a suspension which is treated therein. This type of action is described in an article by Eugen Feifel entitled Zyklonentstaubung-Der Zyklon als Wirbelsenke" (Dust Extraction by Means of a cyclone 'ihe Cyclone as a Vortex Sink) published in the March-April 1938 issue 01' "Forschung auf dem 690, August 8, 1946 a J 1117 21, 1962 Gebiete des Ingenieurwesens," published in Berlin, Germany. The

also by the dimensions of the In the accompanying drawing:

Figure 1 shows diagrammatically in axial section a form of cyclone such as shown in said Driessen article, and

Figures 2 to 6 are graphs illustrating characteristics of separating actions.

The cyclone ill is here shown, Figure 1, as disposed on a vertical axis. It includes a shallow top cylindrical portion II and a lower conical portion l2. Portion I I has a top central opening i3, and debouching into this portion at It is a tangential delivery conduit Ii. Portion I! has an apex opening it restricted by means such as shown in Figure 18 or said Driessen article.

If, for instance, a suspension or loess in water is thickened withthe help of a cyclone, the fraction which is discharged at the apex contains the larger particles, whereas the fraction leaving the cyclone at the opposite end contains only the smaller particles because the specific gravity 01' all particles is the same. If, on the contrary, a gas containing fiy-ashes consisting or diilerent specific gravity and different grain size is cleaned by means or a cyclone, there is found in the dust caught at the apex besides particles of higher specific gravity, larger particles of lower specific gravity, whereas the cleaned gas, leaving the cyclone at the opposite end, contains besides the particles, also very small particles 01 higher specific gravity. Only in cases where all the particles suspended in the gas are of the same grain size would a separation according to specific gravity be effected in the cyclone. The characteristic performance of a cyclon can be represented by a curve as shown in Figure 2, whereas a device separating exactly according to specific gravity can be represented by Figure 3. A device separating exactly according to grain size, such as a screen, is represented by Figure 4.

In Figure 2 the particles leaving at the apex are those to the left of and above the line II,

auaese 3 those leaving at the top being at the other side oi the line. In Figure 3 the sinking particles are above line it and the floating particles below. In Figure 4 the particles to the left of line I! are those held on the screen while those to the right of the line are passed.

Hitherto the cyclone could not be used to separate a mixture of solid materials of difierent specific gravity and diflerent particles size.

The present invention, however, enables the characteristic performance of a cyclone to be changed in such a way that it becomes possible to separate from a mixture oi solid materials of different specific gravity and different grain size a fraction consisting only of particles below or above a certain specific gravity (the specific gravity of separation). According t t vention the mixture to be separated is treated in a cyclone with so much fine material of a specific gravity higher than the specific gravity of separation, that the fraction leaving the cyclone at the apex contains practically no particles of a lower specific gravity than the specific gravity of separation.

If enough very fine particles of a specific gravity higher than the specific gravity of separation are present in the suspension the concentration of this suspension in the apex of the becomes so high that the particles of a specific gravity below the specific gravity oi. separation, irrespective of their dimensions, are obstructed from leaving the cyclone at the apex. By these means the result is attained that the fraction discharged at the apex contains practically only particles of a specific gravity higher than the specific gravity of separation. The characteristic performance of the cyclone can now be represented as given in Figure 5.

The fraction leaving the cyclone opposite the apex now contains besides the particles of a specific gravity below the specific gravity of separation. a small part of the particles of a. higher specific gravity than the specific gravity of separation. However, these are only the very small particles. According to the invention and the method described above, it is possible to obtain with the help of the cyclone besides fractions of a specific gravity above the specific gravity of separation, those fractions having a specific gravity below the specific gravity of separation.

This can be effected by removing the very fine particles from the fraction which leaves the cyclone opposite the apex. A simple way for this purpose is for instance screening. This process is of particular importance for the washing of Figure 6 represents the above described process. Curve ABC shows the normal characteristic performance of the cyclone. By the process according to the invention, a characteristic peri'ormance along BBC is obtained. The area 20 represents the fraction which is discharged at the apex of the cyclone containing only particles above the specific gravity of separation. The fraction discharged the cyclone at the opposite end is represented by the curve DBCFA. By removing the very small particles, for instance by screening. a fraction is leit which contains only particles below the specific gravity of separation, r;presented by area 21 (ADBE). From the fraction containing the very small particles and represented by area 22 (EBCF) the useful parts can be regained, for instance in the preparation of coal, if so desired. with a known process such as froth flotation.

The invention will be illustrated by the following example:

Raw fine coal 0-15 mm. to which loess is added in the proportion 1 part of loess to 2 parts of coal is treated with water in a cyclone having a maximum inner dia. of 200 mm. and a maximum height of 470 mm. The lighter fraction, leaving the cyclone opposite the apex is screened on mm. and shows the following analysis:

Spec. gravityuptnl.3 1.3-1.35 1.35-l.4 1.4-1.45 1.45-1.13 Pei cent-- li2.3 20. 4 9. 1 7.23 5. 97 Spec. gravity 1. 5-1. 55 1. 55-1. 6 above 1.6 Per cent.--- 4. 92 0 0 The analysis of the product leaving the cyclone at the apex is as follows:

Spec. gravity up to 1. 3 1.51-1.35 1.351. t 1.4-1. 1. -1. 5 Per cent 0 0 o 0 595 Spec. gravity 1. 5-1. 1.55-1. a above 1. 6 Per cent 3.04 5. 5 90. 7

In drawing the Tromp curve the specific gravity of separation is found to be 1.54. With this small cyclone a capacity of 7.5 ton/h. washed coal is attained. Besides loess other heavy media such as fine sand, magnetite, barytes and similar materials. or mixtures of such heavy media can be used.

We claim:

1. The continuous method of separating solid particles of different specific gravity and particle size comprising feeding under pressure tangentially into one end portion or a confined circular space a suspension in a liquid of a mass of such particles to move in a cyclonic vortex witho in the circular space wherein centrifugal forces will be substantially in excess of gravitatienal forces, a portion of the mass of particles being of substantially finer size than the remainder of the particles and of a specific gravity higher than c. predetermined specific gravity of separation, discharging liquid and separated particles under pressure created by said feed from two outlets coaxial of the circular space, one of the outlets opening directly from the end portion of the space which is adjacent the point of inieed while the second outlet is located at the non-infeed end of the circular space, saidportion of substantially finer particles being supplied in such quantity and the discharge from the second outlet being so restricted that a concentration of the substantially finer and higher specific gravity particles will be created and maintained in a zone adjacent the second outlet oi. the circular space to obstruct discharge of the particles of a specific gravity lower than said specific gravity of separation from the second discharge outlet so that the fraction discharged from said first discharge outlet will contain substantially all particles of a specific gravity lower than said specific gravity of separation and the fraction discharged at the second discharge outlet will contain substantially only particles of a specific gravity higher than said specific gravity or separation. v

2. A method of the character. described in claim 1 wherein the suspension is fed into the base end portion of a conical circular space.

3. A method of the character described in claim 2 wherein the second discharge outlet is at the apex of the space.

4. The continuous method of separating solid particles of diilerent specific gravity and particle size comprising feeding under pressure tangentially into one end portion or a confined circular spaceasuspensicninaliquidofamassoisuch particles to move in a cyclonic vortex within the circular space wherein centrifugal forces will be substantially in excess of gravitational forces, a

portion or the mass of particles being or substantially finer size than, and of a material foreign to, the remainder of the particles and of a specific gravity higher than a predetermined specific gravity of separation, discharging liquid and separated particles under pressure created by said feed from two outlets coaxial oi the circular space, one of the outlets opening directly from the end portion of the space which is adjacent the point of infeed while the second outlet is located at the non-inieed end of the circular space, such particles of foreign material being added in such quantity and the discharge from the second outlet being so restricted that a concentration of the substantially finer and higher specific gravity particles will be created and maintained in a zone adiacent the second outlet of the circular space to obstruct discharge of the particles of a specific gravity lower than said specific gravity oi separation from the second discharge outlet so that the fraction discharged from said first discharge outlet will contain substantially all particles of a specific gravity lower than said specific gravity of separation and the fraction discharged at the second discharge outlet will contain substantially only particles of a specific gravity higher than said specific gravity of separation.

5. A method or the character described in claim 4 wherein the suspension is led into the base end portion of a conical circular space.

6. A method of the character described in claim 5 wherein the second discharge outlet is at the apex of the space.

7. The method of separating solid particles of diiferent specific gravity into fractions comprising mixing the particles to be separated with a liquid and particles of a size substantially finer than, and of a material foreign to, the bulk of the particles to be separated and having a specific gravity higher than a predetermined specific gravity of separation, feeding under pressure the resultant suspension tangentially into one end portion of a confined circular space to move in a cyclonic vortex within the circular space wherein centrifugal forces will be substantially in excess of gravitational forces, discharging liquid and separated particles under pressure created by said feed from two outlets coaxial of the circular space, one oi the outlets opening directly from the end portion of the space which is adjacent the point of infeed while the second outlet 'is located at the non-infeed end of the circular space. said portion of substantially finer particles being added in such quantity and the discharge from the second outlet being so restricted that a concentration of the substantially finer and higher specific gravity particles will be created and maintained in a zone adJacent the second outlet of the circular space to obstruct discharge of the particles of a specific gravity lower than said specific gravity of separation from the second discharge outlet so that the fraction discharged from said first discharge outlet will contain substantially all particles or a specific gravity lower than said specific gravity or separation and the fraction discharged at the second discharge outlet will contain substantially only particles of a specific gravity higher than said specific gravity of separation.

8. A method of the character described in claim '7 wherein the suspension is fed into the base end portion of a conical circular space.

9. A method of the character described in claim 8 wherein the second discharge outlet is at the apex of the space.

G. DRIESSEN. CEN'IINUS KRIJGSMAN. JAN N. J. LEEMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,149,463 Pardee Aug. 10, 1915 1,197,946 Pardee Sept. 12, 1916 1,392,401 Chance Oct. 4, 1921 1,829,182 Stull May 1'1, 1927 2,052,004 Remlck Aug. 25, 1936 2,104,537 Ellis Jan. 4, 1939 2,287,115 McCluskey June 23, 1942 2,364,799 Laughlin Dec. 12, 1944 

